We have coupled a Michrome microbore HPLC instrument directly to our Finnigan LCQ electrospray ionization mass spectrometer to allow us to perform on-line HPLC - mass spectrometry. We are continuing to evaluate and improve the performance of the system, and are currently evaluating the sensitivity that we can achieve with very narrow bore capillary HPLC separations At the same time, we are optimizing high sensitivity MS/MS sequencing on the LCQ.